Motion estimation is a widely used technique to find or estimate the motion in image processing. For example, if there are two 2-dimensional images, in order to find a motion between these two images, a Sum of Absolute Differences (SAD) calculation is able to be applied on an m×n matching area with a search range of +/−k and +/−l in horizontal and vertical directions respectively, and then the position which yields the smallest SAD is able to be found. FIG. 1 illustrates an example of 2-dimensional motion estimation.